The stability of voters’ partisan choices from election to election is a key feature of democratic politics, but why it varies across advanced industrial democracies and elections is not well understood. This study makes several key contributions to explaining electoral volatility. Firstly, it is argued and demonstrated that strategic voting plays an independent role in inducing vote switching. Secondly, the analysis shows that demand-side factors—such as socio-economic cleavages and organizations—do not predict voter stability, whereas supply-side factors—such as the party system, government performance, and strategic incentives—do. Thirdly, earlier contradictory findings with respect to the role of the electoral system are clarified, as its effects are shown to be indirect rather than direct. And finally, the importance of the temporal dimension to stability is demonstrated, as the time since the previous election is found to have a positive effect on volatility. The results are based on a comprehensive statistical analysis of 336 elections in 21 countries between 1950–2005, where the significance as well as the robustness of individual variables across different model specifications inform the conclusions